1. Field of the Invention
This invention relates to solid-state light emitting devices with photoluminescence wavelength conversion and in particular, although not exclusively, white light emitting devices based on LEDs (Light Emitting Diodes) that are used to excite two or more phosphor materials that are located remote to the LED(s). The invention further concerns wavelength conversion components for converting the color (wavelength) of light generated by the solid-state light emitter.
2. Description of the Related Art
White light emitting LEDs (“white LEDs”) are known in the art and are a relatively recent innovation. It was not until LEDs emitting in the blue/ultraviolet part of the electromagnetic spectrum were developed that it became practical to develop white light sources based on LEDs. As taught, for example in U.S. Pat. No. 5,998,925, white LEDs include one or more phosphor materials, that is photo-luminescent materials, which absorb a portion of the radiation emitted by the LED and re-emit radiation of a different color (wavelength). Typically, the LED chip or die generates blue light and the phosphor(s) absorbs a percentage of the blue light and re-emits yellow light or a combination of green and red light, green and yellow light, green and orange or yellow and red light. The portion of the blue light generated by the LED that is not absorbed by the phosphor combined with the light emitted by the phosphor provides light which appears to the human eye as being nearly white in color.
Due to their long operating life expectancy (>50,000 hours) and high luminous efficacy (70 lumens per watt and higher) high brightness white LEDs are increasingly being used to replace conventional fluorescent, compact fluorescent and incandescent light sources.
Typically a mixture of phosphor materials is provided as a single layer on the light emitting surface of the LED die. Alternatively the different phosphor materials can be provided as respective layers overlying the LED die.
As disclosed in United States patent application US 2008/02118992 A1 to Li, it is also known to provide the phosphor material as a layer on, or incorporate the phosphor material within an, optical component that is located remotely to the LED die.
It is an object of the present invention to provide a light emitting device that in part at least overcomes the limitations of the known devices.